Abstract

Theoretical and experimental aspects of the diffraction of gaussian laser beams by the straight edge bounding an opaque plane are investigated. Theoretical analysis is based upon the Kirchhoff scalar wave theory in the Fresnel limit, assuming an incident electromagnetic field having spatial amplitude and phase variation appropriate to a fundamental-mode gaussian beam. Experimental observation consisting of irradiance as a function of position is in good agreement with this theory. Both theoretical and experimental results are found to depend strongly on gaussian-beam parameters.

From a superficial examination of Fig. 2, it appears that diffraction in the limit of small beam sizes is not purely an edge effect as predicted by Huygens' principle. It is possible to show, however, (see Refs. 6, 7, 22) that, even for small incident beams, diffraction is an edge effect. The size and rate of expansion of the beam play ever-increasing roles in determining the exact nature of the diffraction pattern as the beam size is reduced.

From a superficial examination of Fig. 2, it appears that diffraction in the limit of small beam sizes is not purely an edge effect as predicted by Huygens' principle. It is possible to show, however, (see Refs. 6, 7, 22) that, even for small incident beams, diffraction is an edge effect. The size and rate of expansion of the beam play ever-increasing roles in determining the exact nature of the diffraction pattern as the beam size is reduced.